Industrial Machinery Repair Part Episode 2 Part 1 pptx

234 Couplings are used to contain the lubricant and seal out the entry of contaminants. The sleeves have lubrication holes, which permit flushing and relubrication without disturbing the sleeve gasket or seals. Material-Flexing Couplings Material-flexing couplings are designed to be lubrication free. Combination Couplings Combination (metallic-grid) couplings are lubricated in the same manner as mechanical-flexing couplings. Periodic Inspections It is important to perform periodic inspections of all mechanical equip- ment and systems that incorporate rotating parts, including couplings and clutches. Mechanical-Flexing Couplings To maintain coupling reliability, mechanical-flexing couplings require peri- odic inspections on a time- or condition-based frequency established by the history of the equipment’s coupling life or a schedule established by the predictive maintenance engineer. Items to be included in an inspec- tion are listed below. If any of these items or conditions is discovered, the coupling should be evaluated to determine its remaining operational life or repaired/replaced. ● Inspect lubricant for traces of metal (indicating component wear). ● Visually inspect coupling mechanical components (roller chains and gear teeth, and grid members) for wear and/or fatigue. ● Inspect seals to ensure they are pliable and in good condition. They must be installed properly in the sleeve with the lip in good contact with the hub. ● Sleeve flange gaskets must be whole, in good condition, clean, and free of nicks or cracks. ● Lubrication plugs must be clean (to prevent the introduction of contam- inants to the lubricant and machine surfaces) before being installed and must be torqued to the manufacturer’s specifications. Couplings 235 ● Setscrews and retainers must be in place and tightened to manufacturer’s specifications. ● Inspect shaft hubs, keyways, and keys for cracks, breaks, and physical damage. ● Under operating conditions, perform thermographic scans to determine temperature differences on the coupling (indicates misalignment and/or uneven mechanical forces). Material-Flexing Couplings Although designed to be lubrication-free, material-flexing couplings also require periodic inspection and maintenance. This is necessary to ensure that the coupling components are within acceptable specification limits. Periodic inspections for the following conditions are required to main- tain coupling reliability. If any of these conditions are found, the cou- pling should be evaluated to determine its remaining operational life or repaired/replaced. ● Inspect flexing element for signs of wear or fatigue (cracks, element dust, or particles). ● Setscrews and retainers must be in place and tightened to manufacturer’s specifications. ● Inspect shaft hubs, keyways, and keys for cracks, breaks, and physical damage. ● Under operating conditions, perform thermographic scans for tempera- ture differences on the coupling, which indicates misalignment and/or uneven mechanical forces. Combination Couplings Mechanical components (e.g., grid members) should be visually inspected for wear and/or fatigue. In addition to the items for mechanical-flexing cou- plings, the grid members on metallic-grid couplings should be replaced if any signs of wear are observed. Rigid Couplings The mechanical components of rigid couplings (e.g., hubs, bolts, compres- sion sleeves and halves, keyways, and keys) should be visually inspected 236 Couplings for cracks, breaks, physical damage, wear, and/or fatigue. Any component having any of these conditions should be replaced. Keys, Keyways, and Keyseats A key is a piece of material, usually metal, placed in machined slots or grooves cut into two axially oriented parts in order to mechanically lock them together. For example, keys are used in making the coupling con- nection between the shaft of a driver and a hub or flange on that shaft. Any rotating element whose shaft incorporates such a keyed connection is referred to as a keyed-shaft rotor. Keys provide a positive means for trans- mitting torque between the shaft and coupling hub when a key is properly fitted in the axial groove. The groove into which a key is fitted is referred to as a keyseat when referring to shafts, and a keyway when referring to hubs. Keyseating is the actual machine operation of producing keyseats. Keyways are normally made on a keys eater or by a broach. Keyseats are normally made with a rotary or end mill cutter. Figure 11.15 is an example of a keyed shaft that shows the key size versus the shaft diameter. Because of standardization and interchangeability, keys are generally proportioned with relation to shaft diameter instead of torsional load. The effective key length, “L” is that portion of key having full bearing on hub and shaft. Note that the curved portion of the keyseat made with a Top view End mill cutter Top view L L Rotary cutter Figure 11.15 Keyed shaft: key size versus shaft diameter Couplings 237 TOP VIEWS Square ends Square and round Rounded ends Gib head taper Plain taper SIDE VIEWS Figure 11.16 Key shapes rotary cutter does not provide full key bearing, so “L” does not include this distance. The use of an end mill cutter results in a square-ended keyseat. Figure 11.16 shows various key shapes: square ends, one square end and one round end, rounded ends, plain taper, and gib head taper. The majority of keys are square in cross section, which are preferred through 4 1 2 " diame- ter shafts. For bores over 4 1 2 " and thin wall sections of hubs, the rectangular (flat) key is used. The ends are either square, rounded or gib-head. The gib-head is usually used with taper keys. If special considerations dictate the use of a keyway in the hub shallower than the preferred square key, it is recommended that the standard rectangular (flat) key be used. Hub bores are usually straight, although for some special applications taper bores are sometimes specified. For smaller diameters, bores are designed for clearance fits, and a setscrew is used over the key. The major advantage of a clearance fit is that hubs can be easily assembled and disassembled. For larger diameters, the bores are designed for interference fits without setscrews. For rapid-reversing applications, interference fits are required. The sections to follow discuss determining keyway depth and width, key- way manufacturing tolerances, key stress calculations, and shaft stress calculations. Determining Keyway Depth and Width The formula given below, along with Figure 11.17, Table 11.2 (square keys), and Table 11.3 (flat keys), illustrates how the depth and width of standard 238 Couplings Shafts Hubs H/2 S = DϪYϪH 2 T = DϪYϩHϩ C H /2 W D D Y Y T S 2 Figure 11.17 Shaft and hub dimensions square and flat keys and keyways for shafts and hubs are determined. Y = D −  D 2 − W 2 2 Where: C = Allowance or clearance for key, inches D = Nominal shaft or bore diameter, inches H = Nominal key height, inches W = Nominal key width, inches Y = Chordal height, inches Note: Tables 11.2 and 11.3 shown below are prepared for manufacturing use. Dimensions given are for standard shafts and keyways. Keyway Manufacturing Tolerances Keyway manufacturing tolerances (illustrated in Figure 11.18) are referred to as offset (centrality) and lead (cross axis). Offset or centrality is referred Couplings 239 Table 11.2 Standard square keys and keyways (inches)* Keyways Diameter of holes (inclusive) Width Depth Key stock 5/16 to 7/16 3/32 3/64 3/32 × 3/32 1/2 to 9/16 1/8 1/16 1/8 × 1/8 5/8 to 7/8 3/16 3/32 3/16 × 3/16 1 5/16 to 11/4 1/4 1/8 1/4 × 1/4 1 5/16 to 13/8 5/16 5/32 5/16 × 5/16 1 7/16 to 13/4 3/8 3/16 3/8 × 3/8 1 13/16 to 21/4 1/2 1/4 1/2 × 1/2 2 5/16 to 23/4 5/8 5/16 5/8 × 5/8 2 13/16 to 31/4 3/4 3/8 3/4 × 3/4 3 5/16 to 33/4 7/8 7/16 7/8 × 7/8 3 13/16 to 4 1/2 1 1/2 1 × 1 Source: The Falk Corporation *Square keys are normally used through shaft diameter 4 1 2 "; larger shafts normally use flat keys. to as dimension “N”; lead or cross axis is referred to as dimension “J.” Both must be kept within permissible tolerances, usually 0.002 inches. Key Stress Calculations Calculations for shear and compressive key stresses are based on the following assumptions: 1 The force acts at the radius of the shaft. 2 The force is uniformly distributed along the key length. 3 None of the tangential load is carried by the frictional fit between shaft and bore. The shear and compressive stresses in a key are calculated using the following equations (see Figure 11.19): Ss = 2T (d)x(w )x(L) Sc = 2T (d)x(h 1 )x(L) 240 Couplings Table 11.3 Standard flat keys and keyways (inches) Keyways Diameter of holes (inclusive) Width Depth Key stock 1/2 to 9/16" 1/8 3/64 1/8 × 1/32 5/8 to 7/8" 3/16 1/16 3/16 × 1/8 1 5/16 to 1 1/4" 1/4 3/32 1/4 × 3/16 1 5/16 to 1 3/8" 5/16 1/8 5/16 × 1/4 1 7/16 to 1 3/4" 3/8 1/8 3/8 × 1/4 1 13/16 to 2 1/4" 1/2 3/16 1/2 × 3/8 2 5/16 to 2 3/4" 5/8 7/32 5/8 × 7/16 2 13/16 to 3 1/4" 3/4 1/4 3/4 × 1/2 3 5/16 to 33/4" 7/8 5/16 7/8 × 5/8 3 13/16 to 4 1/2" 1 3/8 1 × 3/4 4 9/16 to 5 1/2" 1 1/4 7/16 1 1/4 × 7/8 5 9/16 to 6 1/2" 1 1/2 1/2 1 1/2 × 1 6 9/16 to 7 1/2" 1 3/4 5/8 1 3/4 × 11/4 79/16to9" 2 3/4 2× 11/2 9 1/16 to 11" 2 1/2 7/8 2 1/2 × 13/4 11 1/16 to 13" 3 1 3 × 2 13 1/16 to 15" 3 1/2 1 1/4 3 1/2 × 21/2 15 1/16 to 18" 4 1 1/2 4 × 3 18 1/16 to 22" 5 1 3/4 5 × 31/2 22 1/16 to 26" 6 4 26 1/16 to 30" 7 5 Source: The Falk Corporation Where: d = Shaft diameter, inches (use average diameter for taper shafts) h 1 = Height of key in the shaft or hub that bears against the keyway, inches. Should equal h 2 for square keys. For designs where unequal portions of the key are in the hub or shaft, h 1 is the minimum portion. Couplings 241 Offset or centrality Shaft Bore Keyseat N C C C C Lead or cross axis (a) (b) Shaft Keyseat Keyseat Bor e Lead Lead C C C C Figure 11.18 Manufacturing tolerances: offset and lead hp = Power, horsepower L = Effective length of key, inches rpm = Revolutions per minute Ss = Shear stress, psi Sc = Compressive stress, psi T = Shaft torque, lb-in or hp × 63000 rpm w = Key width, inches 242 Couplings d Shaft diameter Clearance h 2 h 1 W H Figure 11.19 Measurements used in calculating shear and compressive key stress Table 11.4 Allowable stresses for AISI 1018 and AISI 1045 Allowable stresses - psi Heat Material treatment Shear Compressive AISI 1018 None 7,500 15,000 AISI 1045 255–300 Bhn 15,000 30,000 Source: The Falk Corporation Key material is usually AISI 1018 or AISI 1045. Table 11.4 provides the allowable stresses for these materials. Example: Select a key for the following conditions: 300 hp at 600 rpm; 3" diameter shaft, 3 4 " × 3 4 " key, 4" key engagement length. T = Torque = hp × 63,000 rpm = 300 × 63,000 600 = 31,500 in-lbs Ss = 2T d × w × L = 2 × 31,500 3 × 3/4 × 4 = 7,000 psi Sc = 2T d × h 1 × L = 2 × 31,500 3 × 3/8 × 4 = 14,000 psi The AISI 1018 key can be used since it is within allowable stresses listed in Table 11.4 (allowable Ss = 7,500; allowable Sc = 15,000). Couplings 243 Note: If shaft had been 2- 3 4 " diameter (4" hub), the key would be 5 8 " × 5 8 ", Ss = 9,200 psi, Sc = 18,400 psi, and a heat-treated key of AISI 1045 would have been required (allowable Ss = 15,000, allowable Sc = 30,000). Shaft Stress Calculations Torsional stresses are developed when power is transmitted through shafts. In addition, the tooth loads of gears mounted on shafts create bending stre- sses. Shaft design, therefore, is based on safe limits of torsion and bending. To determine minimum shaft diameter in inches: Minimum shaft diameter = 3  hp × 321000 rpm × Allowable stress Example: hp = 300 rpm = 30 Material = 225 Brinell From Figure 11.20 at 225 Brinell, allowable torsion = 8,000 psi Minimum shaft diameter = 3  300 × 321000 30 × 8000 = 3 √ 402 = 7. 38 inches From Table 11.5, note that the cube of 7 1 4 " is 381, which is too small (i.e., <402) for this example. The cube of 7 1 2 " is 422, which is large enough. To determine shaft stress, psi: Shaft stress = hp × 321,000 rpm × d 3 Example: Given 7 1 2 " shaft for 300 hp at 30 rpm Shaft stress = 300 × 321,000 30 × (7 − 1/2) 3 = 7,600 psi Note: The 7 1 4 " diameter shaft would be stressed to 8420 psi. [...]... 3/4 D3 D D3 D D3 1. 00 1. 95 3.38 5.36 8.00 11 .39 15 .63 20 .80 27 .00 34.33 42. 88 52. 73 64.00 76.77 91. 13 10 7 .2 5 5 1/ 4 5 1 /2 5 3/4 6 6 1/ 4 6 1 /2 6 3/4 7 7 1/ 4 7 1 /2 7 3/4 8 8 1/ 4 8 1 /2 8 3/4 12 5 .0 14 5 16 6.4 19 0 .1 21 6 24 4 27 5 308 343 3 81 422 465 5 12 5 62 614 670 9 9 1 /2 10 10 1 /2 11 11 1 /2 12 12 1 /2 13 14 15 16 17 18 19 20 729 857 10 00 11 57 13 31 1 520 1 728 19 53 21 97 27 44 3375 4096 4 913 58 32 6859 8000 Source:... (psi) 24 4 Couplings 24 000 20 000 g din n Be 16 000 n Torsio 12 0 00 8000 4000 16 0 20 0 24 0 28 0 320 360 400 440 20 0 22 0 Brinell hardness 80 10 0 12 0 14 0 16 0 18 0 Tensile strength, 10 00 psi (Approx.) Figure 11 .20 Allowable stress as a function of Brinell hardness Table 11 .5 Shaft diameters (inches) and their cubes (cubic inches) D 1 1 1/ 4 1 1 /2 1 3/4 2 2 1/ 4 2 1 /2 2 3/4 3 3 1/ 4 3 1 /2 3 3/4 4 4 1/ 4 4 1 /2 4 3/4... simple Figure 12 . 2 illustrates a typical cross-section of a cyclone separator, which Clean-gas outlet Dust shave-off Pattern of dust stream (principally the finer particles) following eddy current Shave-off-dust channel Inlet for dust-laden gases Shave-off-reentry opening Pattern of coarser dust mainstream Dust outlet Figure 12 . 2 Flow pattern through a typical cyclone separator Dust Collectors 25 5 consists... located below the tube sheet Dust Collectors 24 7 Bag support and shaking mechanism Clean gas side Dirty gas side Dust discharge Figure 12 . 1 A typical baghouse For continuous operation, the filter must be constructed with multiple compartments This is necessary so that individual compartments can be sequentially taken offline for cleaning while the other compartments continue to operate Ordinary shaker-cleaned... K1 may be more than 10 times the value of the resistance coefficient for the original clean fabric If 1 the depth of the dust layer on the fabric is greater than about 16 " (which 2 ), the prescorresponds to a fabric dust loading on the order of 0 .1 lbm/ft sure drop across the fabric, including the dust in the pores, is usually negligible relative to that across the dust layer alone In practice, K1... 8000 Source: The Falk Corporation 12 Dust Collectors The basic operations performed by dust-collection devices are: (1) separating particles from the gas stream by deposition on a collection surface, (2) retaining the deposited particles on the surface until removal, and (3) removing the deposit from the surface for recovery or disposal The separation step requires: (1) application of a force that produces... The pressure drop across the fabric media and the dust layer may be expressed by: p = K1 Vf + K2 ω Vf Where: p = pressure drop (inches of water) V f = superficial velocity through filter (feet/minute) ω = dust loading on filter (lbm/ft2 ) K1 = resistance coefficient for conditioned fabric (inches of water/foot/ minute) K2 = resistance coefficient for dust layer (inches of water/lbm/foot/ minute) Conditioned... bag and exit to the clean side, or it may flow through the bag from its outside and exit through the tube’s opening Figure 12 . 1 illustrates a typical baghouse configuration Fabric-filter designs fall into three types, depending on the method of cleaning used: (1) shaker-cleaned, (2) reverse-flow-cleaned, and (3) reversepulse-cleaned Shaker-Cleaned Filter The open lower ends of shaker-cleaned filter bags... the particles relative to the gas, and (2) sufficient gasretention time for the particles to migrate to the collecting surface Most dust-collections systems are comprised of a pneumatic-conveying system and some device that separates suspended particulate matter from the conveyed air stream The more common systems use either filter media (e.g., fabric bags) or cyclonic separators to separate the particulate... inlet-gas velocity and density by: hvt = 0.0030ρV2 c 25 6 Dust Collectors Where: hvt = Inlet-velocity head (inches of water) ρ = Gas density (lb/ft3 ) Vc = Average inlet-gas velocity (ft/sec) The cyclone friction loss, Fcv , is a direct measure of the static pressure and power that a fan must develop It is related to the pressure drop by: Fcv = pcv + 1 − 4Ac 2 π D2 e Where: Fcv pcv Ac De = Friction loss (inlet-velocity . inches) DD 3 DD 3 DD 3 1 1.00 5 12 5 .0 9 729 1 1/4 1. 95 5 1/ 4 14 5 9 1 /2 857 1 1 /2 3.38 5 1 /2 16 6.4 10 10 00 1 3/4 5.36 5 3/4 19 0 .1 10 1 /2 11 57 2 8.00 6 21 6 11 13 31 2 1/ 4 11 .39 6 1/ 4 24 4 11 1 /2 1 520 2 1 /2 15 .63 6 1 /2. 1 /2 × 13 /4 11 1/ 16 to 13 " 3 1 3 × 2 13 1/ 16 to 15 " 3 1 /2 1 1/4 3 1 /2 × 21 /2 15 1/ 16 to 18 " 4 1 1 /2 4 × 3 18 1/ 16 to 22 " 5 1 3/4 5 × 31 /2 22 1/ 16 to 26 " 6 4 26 1/ 16 to. 9 /16 to 5 1 /2& quot; 1 1/4 7 /16 1 1/4 × 7/8 5 9 /16 to 6 1 /2& quot; 1 1 /2 1 /2 1 1 /2 × 1 6 9 /16 to 7 1 /2& quot; 1 3/4 5/8 1 3/4 × 11 /4 79 /16 to9" 2 3/4 2 11 /2 9 1/ 16 to 11 " 2 1 /2 7/8 2 1/ 2